This invention relates to rotary lawn motors and particularly to cutting apparatus for use with rotary lawn mowers to improve their safety and effectiveness.
Rotary lawn mowers having horizontally-oriented, radially-disposed blades rotated by an engine with a vertically-oriented drive shaft are well known. Typically, the cutting element of such lawn mowers comprises an elongate flat steel blade which is securely attached at its center to the vertical shaft so that the blade rotates in a horizontal plane. The trailing edge of the blade may be slightly upturned so that the blade produces an upward draft tending to raise grass to a vertical position for cutting, for example, as shown in Halsten U.S. Pat. No. 3,959,954, and the leading edges are sharpened for a short distance from each end of the blade for cutting grass.
Properly maintained such a lawn mower effectively cuts grass on even terrain. However, where the ground is bumpy the blade tips often cut extremely close to the ground, "scalping" the lawn and picking up small pebbles or sticks, which nick and dull the cutting edges, and the blades may even strike the ground, causing the engine to stall. More importantly, because of the high speed of the rotating tips of such a lawn mower blade, any stones, sticks, or other debris which are picked up by the blade are very likely to be expelled at a great velocity, endangering the operator or bystanders. In addition, if the grass is very tall then it may be too heavy to be entirely lifted by the suction of a conventional blade and the lawn mower itself may push the grass down as it rolls over the grass, with the result that the grass is cut unevenly. Further, it is often desirable, especially when mowing tall grass, to chop the grass finely as it is being cut, and to distribute the cuttings over the trimmed lawn as mulch, which is not very well accomplished by conventional rotary mowers.
Althougn some attempts have been made to overcome the aforementioned problems of conventional rotary mowers, none has been successful in overcoming all of the problems. For example, Watrous U.S. Pat. No. 2,669,826 discloses a skid disposed below the center of its rotary blade to space the blade from the ground, but the skid fails to prevent the blade from scalping the lawn or picking up small rocks due to tipping of the blade where the ground is uneven or bumpy since there is only one point of contact of the skid with the ground. Philips, Jr., et al U.S. Pat. No. 2,953,888 and Messner U.S. Pat. No. 3,905,181 disclose rotary blade mechanisms which include a bottom cover over a part of their respective blades which would reduce the tendency of the blades to scalp the ground and thrown debris, but in order to cut grass a large area of blades is left uncovered and the function of those covers is to contain grass after it has been cut, rather than to prevent the entry of debris. Geier U.S. Pat. No. 4,051,647 and Watrous, as well as Halsten, disclose blade mechanisms which tend to raise grass to an upright position for cutting; however all of those mechanisms are somewhat limited by their configurations in the amount of updraft that they can produce. In addition, Halsten and Messner disclose specific types of apparatus for mulching grass after it is cut.
Accordingly, there is a need for an improved rotary lawn mower that simultaneously increases operational safety and mower durability, prevents scalping of the grass being cut, raises tall and heavy grass into a cutting element for uniform cutting, and creates a mulch from the cut grass.